Tony Blair might be viewed increasingly at home as a leader with a fast-approaching sell-by date but he is seen differently in Washington, with George Bush urging him last night to stay in power "as long as I'm president".

The comments came during a joint press conference at the White House during which the two leaders alternated between grave statements on Iraq and some light-hearted mutual ribbing.

Midway through the press conference a member of the British press delegation asked Mr Blair if it was "possibly your last official visit to Washington as prime minister", also quizzing Mr Bush about what in particular he would miss about his close ally.

"Hmm - I'll miss those red ties, is what I'll miss," Mr Bush began before adding, more seriously: "I know a man of resolve and vision and courage. And my attitude is, I want him to be here so long as I'm the president."

Mr Blair refused to be drawn, commenting to laughter: "Well, what more can I say? Probably not wise to say anything more at all," before imploring the British press to "ask a few serious questions".

There were some more serious questions, mainly about Iraq, where Mr Bush admitted to "setbacks and missteps" and acknowledged the domestic opposition to the war he now faces.

"The decision to remove Saddam Hussein from power was controversial. We did not find the weapons of mass destruction that we all believed were there - and that's raised questions about whether the sacrifice in Iraq has been worth it," the president said.

Pressed on mistakes in Iraq, Mr Bush admitted some of his rhetoric might have been misjudged. "Saying 'bring it on,' kind of tough talk, you know, that sent the wrong signal to people," he said.

"I learned some lessons about expressing myself maybe in a little more sophisticated manner - you know, 'wanted dead or alive,' that kind of talk."

The leaders also discussed Iran and the UN - the latter bringing up further speculation about Mr Blair's political future.

A questioner referred to the prime minister's speech at Georgetown University later today in which he will call for a reformed UN led by a powerful secretary-general.

"Is that a job application?" Mr Blair was asked. "Do you have someone in mind? And, if not, how are you going to get the reform at the UN you want to see?"

Mr Blair's response was concise: "No, no and I'm not sure is the answer to those ones."

If it was a final joint performance for the leaders they took to it at times like a pair of veteran stand-up comics, Mr Bush ending the press conference by jokingly asking his guest if he could "buy you dinner".

Even on the subject of Iraq, the prime minister introduced some gentle mockery of his host, noting that recent elections in Iraq saw a higher voter turnout than seen when either he or Mr Bush were elected.

"Which one? 2000 or 2004?" Mr Bush asked with a grin, being told in return: "I think both of them."

Mr Blair followed the exchange with an impassioned plea for the world to support democracy in Iraq despite the continued violence, being told at the end by his host: "I'm going to say, that was a great answer."